Fluorocarbon based solvents have been used extensively for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room-temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves the object free of residue. This is contrasted with liquid solvents which leave a residue on the object after rinsing.
A vapor degreaser is used for difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently. The conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.
Recently, nontoxic nonflammable fluorocarbon solvents like trichlorotrifluoroethane have been used extensively in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes, and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts, etc.
The art has looked towards azeotropic compositions having fluorocarbon components because the fluorocarbon components contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic compositions are desired because they exhibit a minimum boiling point and do not fractionate upon boiling. This is desirable because in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Therefore, unless the solvent composition is essentially constant boiling, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. For example, preferential evaporation of the more volatile components of the solvent mixtures would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency toward soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity.
A number of 1,1,2-trichloro-1,2,2-trifluoroethane based azeotrope compositions have been discovered which have been tested and in some cases employed as solvents for miscellaneous vapor degreasing and defluxing applications. For example, U.S. Pat. No. 3,573,213 discloses the azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane and nitromethane; U.S. Pat. No. 3,340,199 discloses an azeotropic composition of 1,1,2-trichloro-1,2,2-trifluoroethane and isopropanol; U.S. Pat. No. 3,789,006 discloses azeotropic mixtures of 1,1,2-trichloro-1,2,2-trifluoroethane, isopropanol, and nitromethane; U.S. Pat. No. 3,455,835 discloses azeotrope-like compositions of 1,1,2-trichloro-1,2,2-trifluoroethane and trans-1,2-dichloroethylene; U.S. Pat. No. 4,767,561 discloses azeotrope-like compositions containing 1,1,2-trichloro-1,2,2-trifluoroethane, isopropanol, and trans-1,2-dichloroethylene; U.S. Pat. No. 3,903,009 discloses an azeotropic composition of 1,1,2-trichloro-1,2,2-trifluoroethane, ethanol, and nitromethane; and L. H. Horsley, in Advances in Chemistry Series, No. 35, Azeotropic Data II, 25 (1962), discloses an azeotropic composition of 1,1,2-trichloro-1,2,2-trifluoroethane and ethanol.
The art is continually seeking new fluorocarbon based azeotropic mixtures which offer alternatives for new and special applications for vapor degreasing and other industrial cleaning applications.
Accordingly, it is an object of this invention to Provide novel azeotrope-like compositions based on 1,1,2-trichloro-1,2,2-trifluoroethane which have good solvency power and other desirable properties for vapor degreasing and other solvent cleaning applications.
Another object of the invention is to provide novel constant boiling or essentially constant boiling solvents which, in addition to having the foregoing advantages, are liquid at room temperature and non-fractionating.
A further object of the invention is to provide azeotrope-like compositions which are nonflammable in both the liquid and vapor phases. These and other objects and features of the invention will become apparent from the description which follows.